Infiltrated powdered metal cooking utensil

ABSTRACT

The invention concerns a powdered metal cooking utensil with the powdered metal member having at least a region through which heat is transferred to the material and with the said region being infiltrated by a metal having a higher coefficient for heat conductivity than the powdered metal.

United States Patent [1 1 3,623,630

[72] In en o John E- Ro 2,759,846 8/1956 VOSlCl 29/] 82.1 514 W. Main St., Ligonler, Pa. 15658 3,145.101 8/1964 Franssen 29/182. l [21] Appl. No. 320,145 $171,653 9/1 66 wolf H 220/64 [22] Filed Apr. 29 1969 FORHGN PATENTS [451 Paemed 7s 1 .049 7/1956 Great Britain H 29/1 82.1

720,050 12/1954 Great Britain i v. 29/1821 [54] INFILTRATED POWDERED METAL COOKING Primary Examiner-Carl D. Quarforth TE Assislan! Examiner-B. H. Hunt 5 Claims 8 Drawing g Al!0rne v Melvin A Crosby [52] us. C1 i v 220/64,

29/182L29/1823 511 rm. Cl A47] 27/00 ABSTRACT The memo" a pmvdered ing utensil with the powdered metal member having at least a [so] new of Search region through which heat is transferred to the material and with the said region being infiltrated by a metal having a [56] References Cited higher coefficient for heat conductivity than the powdered UNITED STATES PATENTS 2,323,162 6/l943 Talmage .1 75/208 PAIENTEBuuv 30 Ian 3, 623 630 sum 1 or 2 FIG-I FIG-2 I INVENTOR JOHN E. RODE INFILTRATED POWDERED METAL COOKING U'I'ENSIL This invention relates to articles made by powder metallurgy techniques and is particularly concerned with an article of this nature having novel characteristics imparted thereto by the combining of materials.

The manufacture of articles by powder metallurgy techniques is known and extends to the formation of articles of widely varying configurations and formed of substantially any sort of metal or alloy thereof capable of being reduced to a fine powder and compacted and then sintered to bond the particles together.

Articles formed by powder metallurgy techniques are normally of a porous nature because the particles of metal bond together at the interface thereof during the sintering process forming a skeleton like structure having voids therein. The term bond as used herein describes intermetallic diffusion and the resulting joining of adjacent particles which may or may not take place in the presence of a liquid phase, depending upon the sintering temperature and the specific metallic elements contained in the powder compact. The amount of voids will vary with the particular metal and the degree of compaction thereof prior to sintering and with the temperature and duration of sintering.

It is relatively simple, however, to produce a structure which is 70 to 80 percent or more of the density of the solid form of the same material. More porous structures are obtained when the compacted powder originally consists of uniformly spherical shaped particles of uniform size. Irregularly shaped particles of ductile materials, such as the ferrous alloys, are easily deformed during the compaction which reduces the pore size in the matrix to a greater degree than will occur with smoothly shaped or spherical particles. Also effecting a reduction of pore volume is the presence of relatively fine particles mixed with coarse particles, in which case, the fine particles occupy the spaces between the compacted coarse particles.

The majority of the voids present in a powder compact, formed in the manner described above, are interconnected except when the compaction is performed at extremely high pressures so that pore volume is less than about 7 percent of the total volume. The present invention is primarily concerned with compacts having interconnected voids.

It is also known that the voids in a sintered piece of the nature referred to can be infiltrated with another material in liquid form, for example, another metal or a plastic material. The impregnating material, when cooled or cured to a solid state becomes an integral part of the article and seals the pores and imparts certain characteristics to the infiltrated material different than it had before infiltration. Such a composite is sometimes known as a biskeletal structure, with each integral component present accomplishing specific functions of the material system as will be explained in the following.

With the foregoing in mind, the present invention has a primary objective, the provision of an article of manufacture and a method of making the article in which powder metallurgy techniques are employed for making the article and infiltration and/or impregnating techniques are employed for imparting certain desired characteristics to the article.

A particular object of the present invention is the provision of an article formed by powder metallurgy techniques through which heat is to be transferred and to improve the heat conductivity in the article in at least a certain area thereof by infiltration of the area with a high heat conductivity metal.

A still more specific object of the present invention is the manufacture of cooking vessels, or the like, formed of metal powder, such as stainless steel powder, and having the region thereof through which heat is supplied to the contents of the vessel, ordinarily the bottom thereof, impregnated with copper.

A further object of the invention is the provision of cookware and similar heat-conducting vessels which are less expensive to manufacture than those made according to prior art practices.

A still further object is the provision of cookware and the like made by powder metallurgy techniques which are more efficient with regard to heat consumption, more effective with regard to appropriate heat distribution within the cookware,

and more efficient with regard to time required to transfer heat than conventional cookware.

The foregoing objects and advantages of the present invention will become more apparent upon reference to the following detailed specification, taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view partly in section, showing a simple vessel constructed according to the present invention;

FIG. 2 is a schematic view showing how the powder from which the vessel is made could be compacted by pressing into the form of the vessel;

FIG. 3 schematically illustrates the manner in which a slurry of the powder material of the vessel could be formed by slip casting;

FIG. 4 schematically illustrates the manner in which a slurry of the powdered material could be formed by centrifuging;

FIG. 5 schematically illustrates one manner in which the bottom of the vessel could be infiltrated with copper during or subsequent to sintering of the article;

FIG. 6 illustrates a sheet formed of the powdered material and having a region thereof infiltrated;

FlG. 7 illustrates the manner in which a blank taken from the sheet of FlG. 6 could be formed into a vessel by pressing or drawing; and

FIG. 8 is a sectional view showing still another type of vessel adapted to be manufactured according to the present invention.

Referring to the drawings somewhat more in detail, vessel 10 in FIG. 1 has an upstanding sidewall portion 12 and a bottom 14. According to the present invention the vessel 10 is formed by powder metallurgy techniques utilizing, for example, iron powder or stainless steel powder. Stainless steel powder has obvious advantages in connection with cookware and the like,'because it is corrosion resistant and does not rust and presents a good appearance and is easily cleaned.

The heat conductivity of stainless steel is, however, quite low and it presents a disadvantage in respect to cookware for this reason. Cookware made of iron powders has a somewhat higher heat conductivity than stainless steel, but still lower than that of solid iron, and also lower than copper infiltrated iron powder. For the purpose of the present disclosure, stainless steel will be referred to, but it will be understood that the present invention is applicable to substantially any type of metal powders which can be compacted into useful structures, and have a higher melting point then that of the desired impregnating material.

In FIG. 1, the bottom portion 14 of the vessel, and up to about the dash line 16, is impregnated with copper, or copper alloy. Copper alloys exhibit high heat conductivity and'by infiltrating the bottom of the vessel with this material, the rate of heat transference through the bottom of the vessel is substantially enhanced. The heat conductivity through the sidewalls of the vessel, which would represent heat loss for stove-top cooking, remains that of the powdered metal, and where the powdered metal employed is stainless steel, is substantially lower than that of the bottom of the vessel.

The sidewalls 12 of the vessel may be impregnated with a plastic material, such as polyester resin, or the vessel may be lined as indicated by the layer at 18 with Teflon which is polytetrafluorethylene, or similar plastic material. Either the Teflon lining or the impregnation of the sidewalls of the vessel will seal the porous sidewalls against the passage of any liquids therethrough and will further assure a somewhat lower thermal conductance through said sidewalls. The vessel may have a lid 11, made from powdered metal and impregnated or coated with plastic or infiltrated with metal.

In forming the body of the vessel, the powders may be pressed as shown in FIG. 2, in which die parts 20 and 22 define therebetween a cavity 24 in which the metal powder is disposed. This powder may be admixed with a lubricating material, such as lithium stearate or the like, which assists in causing the powder to flow into the cavity uniformly and to flow within the cavity when the pressing takes place. Some sacrifice is made in the strength of the compacted material in the case of ferrous metal powders when such lubricants are used; however, the enhanced flow characteristic of the material in the die cavity greatly improves the uniformity of the density of the compact which is obtained; and, therefore, the pore volume within the compacted structure.

Sintering of the compact taken from the die cavity takes place at a temperature of about 1,900 to 2,400 F for a period of 2% hour to 1 hours. Sintering temperature is normally controlled to within plus or minus 25 F. and the desired temperature is selected within the above-stated range depending upon the specific alloy and desired sintered properties. The sintering furnace atmosphere is ordinarily reducing or at least nonoxidizing, such as produced by cracked ammonia, hydrogen, or mixtures of hydrogen and carbon monoxide, as is well known in the art. The lubricant will volatilize and dissipate from the compact during the heating and, therefore, will not be present once the sintering temperature is reached.

A known method for infiltrating copper or copper alloys into ferrous metal powder compacts during the sintering process is described in (1.8. Pat. No. 3,307,294 by Arthur B. Michael, dated Mar. 7, 1967. Following the method of this patent, a second compact is pressed from the powder form of the impregnating alloy. This second compact being placed upon the ferrous metal compact over the region to be infiltrated, and the assembly is placed within the sintering furnace. Fusion of the impregnating alloy occurs during the initial stages of sintering and results in a sintered and infiltrated structure at the end of the sintering cycle. Also following this method, the infiltrating material is admixed with a parting compound so that any adhering surface residue on the sintered and infiltrated object may be quickly and simply removed subsequent to sintering. Alternative methods in which the infiltration is carried out subsequent to sintering are discussed in the following FIG. 3 shows a slip mold 26 into which a slurry of the powder is poured so that the liquid fraction of the slurry, usually water, can pass through the mold as indicated by arrows 28 leaving a layer 29 of the powder within the mold. Mold 26 has the form of the cookware vessel to be made and is composed of a refractory material such as aluminum oxide and can, therefore, serve the additional purpose of being the sintering tray or container. The article is removed from the mold after sintering is completed. The infiltration of the workpiece may or may not be accomplished during sintering, as desired.

A variation of this method may be performed whereby an additive is made to the slurry which provides for the function of binding the particles together after drying out of the slurry vehicle solution. Watersoluble stearates can be used for this purpose or the vehicle may be naphtha or a chlorinated hydrocarbon solvent used in conjunction with a parafin wax or methyl methacrylate binder. These binders, or suitable substitutes therefore, permit removal of the compacted powder part from the mold prior to sintering. As in the case where lubricants are used as additives, the binder is volatilized and driven off during the heating to reach the sintering temperature. Except as noted, the article is treated in the same manner as was described for the article removed from the mold arrangement of FIG. 2.

FIG. 4 shows a mold cavity formed by the outer and inner members 30, which is adapted for receiving a slurry of the powder material, with the mold being adapted for being centrifuged to cause the powder to settle out from the slurry and form an article of the shape desired. In FIG. 4, the centrifuge arm 32 is pivoted to the mold arrangement at 34. When arm 32 is driven in rotation at high speed, the mold will pivot outwardly so that the centripetal force on the powder will act toward the bottom of the cavity The time required for complete centrifugal sedimentation depends upon the speed of rotation, the viscosity of the slurry, and the character of the metal particles. When sedimentation is completed the fluid decant, indicated at 31 in FIG. 4, is removed, and the powder sediment allowed to dry. Subsequent processing is accomplished in the same manner as described above for slip casting with an adhesive binder added to the slurry to facilitate removal of the otherwise fragile article from the mold cavity.

In any of the molding arrangements illustrated, suitable parting agents, such as sprayed or preformed films, can be ap plied to the die or mold surfaces to assist in removing the articles from the die or mold and may, in some cases, be necessary due to the fragility of the articles prior to sintering and consequently their propensity to being damaged if they do not separate readily from the mold walls.

FIG. 5 shows a simple arrangement for infiltrating the bottom of the vessel with molten copper alloy. In FIG. 5, 40 represents a container having molten copper alloy therein. The vessel to be infiltrated is indicated at 42 and is mounted on a holder 44 as by clamps 46. Holder 44 has a suction passage 48 extending therethrough communicating with the interior of the vessel and connected by hose 50 with a source of suction. A seal member 52 may be provided about the upper edge of the vessel. The vessel to be infiltrated is subjected to suction and is immersed in the molten copper alloy up to about the level it is desired for the bottom of the vessel to be infiltrated.

After a predetermined time, determined by test and experimentation, and depending upon the thickness of the bottom wall of the vessel and the size of the pores therein, the bottom will be completely infiltrated with copper alloy and the vessel can be removed from the molten alloy and taken from the holder.

In certain cases, depending upon the wetting ability of the infiltrant to the sintered metal, it is not necessary to employ a variance of pressure or suction to induce complete infiltration. In a variation of the above method, a predetermined quantity of the solid form of the infiltrating material is placed within the sintered vessel and the assembly is heated until the infiltrant is melted and infiltrates the sintered structure.

When the entire article is to be infiltrated, it can be placed in a chamber, the chamber evacuated, the article immersed in the molten infiltrant, and the vacuum interrupted.

Certain finishing operations can now be carried out on the vessel and which could include removal of any excess of the infiltrant material on either the inside or the outside of the vessel. Alternatively, any excess of the material could remain in place on the bottom of the vessel as a film coating providing that the appearance and texture is consistent with that desired. The surface film of highly conductive material, if allowed to remain, provides for more uniform heat distribution on the bottom of the vessel which presents an obvious further advantage.

After the bottom wall of the vessel is infiltrated, the sidewalls can be impregnated with plastic, by such techniques as are well known in the art, including vacuum techniques similar to that described in connection with the infiltration of the bottom of the vessel. Such impregnation of the sidewalls with plastic material would seal the sidewalls without, however, modifying the heat conductivity thereof to any substantial degree.

Alternatively, or in addition to the impregnation of the sidewalls, the entire inside of the vessel could be provided with a Teflon film according to well-known practices in this art.

FIG. 6 illustrates a sheet 60 made by powder metallurgy techniques and shown an area 62 which has been infiltrated with a metal, preferably a copper alloy. From this sheet there may be cut a blank of the size indicated by the dashed circle 64 and this blank can be formed into the shape of the vessel as shown at 66 in FIG. 7. Trimming of the formed blank along line 68 will produce the desired vessel. The region of the vessel which forms the sidewall thereof can be impregnated with plastic either before or after the fonning operation, depending upon the extent to which the forming will deform the original powder metal matrix. Large deformations of the porous structure may cause extrusion of some of the impregnant or be impaired by the presence of the impregnant and would, therefore, require that the impregnating of the plastic be carried out after forming of the vessel to shape.

FIG. 8 illustrates an article 70 of cookware having integral with the bottom wall 72 thereof, channels 74 adapted for receiving an electric heating element. The bottom wall up to about the line 76 is infiltrated with a high heat conductivity metal, such as copper alloy, and the sidewalls of the vessel above this line may be impregnated with plastic or the vessel may be lined with a Teflon film, or both, as indicated at 78.

In any case, whether the vessel is used for cookware or other purposes, it is characterized in having a region through which heat is supplied to the vessel which has substantially higher heat conductivity than the basic material of the vessel, while this basic material exhibits a lower heat conductivity in respect of other portions of the vessel than does the heat-conducting wall of the vessel or a solid of the same material.

By the practice of the present invention, the advantages of powder metallurgy techniques in respect to economy can be taken advantage of to produce work members at lower cost than they can be formed from solid material.

It is understood, of course, that the articles can betumed or otherwise machine treated, such as by hot or cold forging in order to shape them following sintering thereof, if desired or necessary. Furthermore, machining operations for attaching legs and handles, and the like, can be performed on the articles the same as if they were made of solid metal. As to finishing techniques, the articles can be burnished, polished, plated, or otherwise treated in order to impart desired surface characteristics thereto, particularly with respect to appearance, according to practices well known in the metal working art.

Certain types of vessels used for cooking and other heating purposes, and which fall within the scope of my invention, are further characterized by specially shaped interior surfaces which are designed to impart correspondingly shaped surfaces to the item being cooked or heated. More specifically, this variation applies where the item being cooked or heated transforms from a liquid, paste or powder form, or consistency, into a solid as a result of or during the heating. Typical examples of such vessels are griddles for cooking waffles and specially shaped omelettes, baking containers for breads and cakes, and curing presses for the making of articles from thermosetting plastic and rubber compositions. Articles in the latter category include automobile tires, silicone rubber electrical connectors, children's toys and the like. Cookware and related heating vessels in which cooking or curing is performed which are made by the powder metallurgy techniques and utilize infiltrated copper alloy or similar heat-conducting metal may be designed for use with external heating sources, such as gas or electric stoves, or may be designed with integral electric heating elements, or may be provided with passages through which a heating fluid is circulated.

Articles having complex configuration, such as, for example, waffle irons or tire molds, can advantageously be made from powdered metals, thereby greatly reducing, or even eliminating machining, and infiltrated with another metal according to the present invention to enhance the heat-conducting properties of the article. The articles are inexpensive to make, are free of warpage and can be completely, or selectively, infiltrated and/0r impregnated to meet particular conditions of use.

Modifications can be made within the scope of the appended claims.

What is claimed is:

l. A cooking utensil comprising a member in the form of a porous skeletal structure of compacted and sintered powdered metal selected from the group consisting essentially of iron and stainless steel and another metal selected from the group consisting essentially of copper and copper alloys infiltrated into said skeletal structure in at least that portion of said article to which heat 18 applied to enhance the heat conductivity of the said portion, said infiltrated metal extending completely through said portion of said cooking utensil.

2. A cooking utensil according to claim 1 which includes a bottom wall part and an upstanding sidewall part and said infiltrated portion comprises at least the entirety of said bottom wall part of said container.

3. A cooking utensil according to claim 2 which includes a nonporous sealant material selected from the group consisting essentially of polyester resin and polytetrafluorethylene applied to said sidewall part of the container.

4. A cooking utensil according to claim 3 in which said sealant material impregnates said sidewall part.

5. A cooking utensil according to claim 3 in which said sealant material is in the form of a film on the inside of said container. 

1. A cooking utensil comprising a member in the form of a porous skeletal structure of compacted and sintered powdered metal selected from the group consisting essentially of iron and stainless steel and another metal selected from the group consisting essentially of copper and copper alloys infiltrated into said skeletal structure in at least that portion of said article to which heat is applied to enhance the heat conductivity of the said portion, said infiltrated metal extending completely through said portion of said cooking utensil.
 2. A cooking utensil according to claim 1 which includes a bottom wall part and an upstanding sidewall part and said infiltrated portion comprises at least the entirety of said bottom wall part of said container.
 3. A cooking utensil according to claim 2 which includes a nonporous sealant material selected from the group consisting essentially of polyester resin and polytetrafluorethylene applied to said sidewall part of the container.
 4. A cooking utensil according to claim 3 in which said sealant material impregnates said sidewall part.
 5. A cooking utensil according to claim 3 in which said sealant material is in the form of a film on the inside of said container. 